Toying with time: Yakir Aharonov's world

[caption id="attachment_118374" align="aligncenter" width="580" caption="Yakir Aharonov receives National Medal of Science from President Obama at the White House Nov. 17."][/caption]

Time flows in two directions. The future is predetermined, but humans have free will. And at the tiniest levels of reality, particles sometimes behave like Lewis Carroll's Cheshire cat -- their physical properties, like the cat's smile, lingering behind when the particles are somewhere else.

A conversation with National Medal of Science winner Yakir Aharonov, a physicist at Chapman University, seems to ricochet around time, the universe, and everything, echoeing from the outer boundaries of science fiction.

But Aharonov is no sci-fi writer. He's working in the real world of physics, and the verified results he's talking about -- measurements revealing that the future can influence the past, or that a particle can be altered by a magnetic field without going anywhere near it -- come straight from the laboratory.

Aharonov, 78, has gained a worldwide reputation as an exacting if unconventional physicist, whose strange findings suggest a radical reinterpretation of time and even of reality itself.

A native of Israel who travels there frequently, Aharonov is known for making a series of "weak measurements" showing that the present could be a kind of collision of influences flowing in two directions: from the past as well as from the future.

He's also known for the Aharonov-Bohm effect, discovered in 1959, in which a charged particle is influenced by a magnetic field with which it has never come into contact.

But the physicist, fond of smoking cigars and telling punchline stories, says he came to Chapman two years ago in part to take advantage of an atmosphere of free inquiry, a place where he could explore the wild landscape of his world-shaking ideas.

Q. Based on your work, how should we change our concept of time?

A. First let me explain how the idea came about from the properties of quantum mechanics -- the suggestion that we should change our notions of time. The basic difference between quantum mechanics and classical physics is that (in quantum physics) two physical systems in exactly the same state, initially, end up later in different states. It means we cannot predict the future exactly. We can only predict probabilities.

When I thought about it, it occurred to me that perhaps what nature or quantum mechanics is trying to tell us is, in fact, that there is already a difference between the two particles, but we can discover the difference only later, in the future. Though they're different already, there's no way to find out until you do the experiment in the future, and find the difference between the two systems.

That suggested to me that if we are trying to understand how to describe the present time, we need not only information of the past that comes to the present, but also, some information from the future (that) comes back to the present that tells us more information about the system.

That is true about microscopic systems in the quantum domain. It suggests perhaps in some future physics, some future theory, we have now an approach to time where the present is described not only by things that happened in the past, (but things that) come back like the movie, Back to the Future -- come back to affect the present.

That's a real change in our understanding of time.

Q. Are you saying that time could flow in both directions -- forward from the past, backward from the future, to create the world we live in moment to moment?

A. If we try to extend these notions to our universe, and say that the universe has a description by two modes -- one mode coming from past history, another mode coming back from the future, the destiny state of the universe, that would indeed be a completely new way of thinking about the universe: saying that everyday things that happen to us (are) not only dictated by the past but also dictated by some destiny that we have to fulfill when we come toward the future.

But this is speculation. I have no proof of that. If we try to extend what we learned to do with quantum mechanical, microscopic systems -- extend it to our universe -- there will be this new description.

Our group (at Chapman) is looking now to find some experiments that can be done on a cosmological scale to see if the universe has a destiny state, not only a history state.

Q. Your recent paper in Physics Today (co-authored with Jeff Tollaksen, also at Chapman, and Sandu Popescu of the University of Bristol) suggests that the universe might have a fully determined final state as well as a beginning state. Does that cause you to wrestle with the idea of free will?

A. I don't have any problem with that because free will means you are only freed from the past. You're not freed from the future. If somebody would know your future, but not tell you about it, and we would not use (the information) in any way, it's as if we waited till the future came.

If something comes back from the future, like this destiny state, to the present, but it is not available to to tell you what this future is, you're still free from the past. You can change your mind. If you change your mind, you change your fate, and it will be the new state.

Q. How can you best describe to a lay audience the implications of 'weak measurements?'

A. The idea is following that (which) was discovered in quantum mechanics. It comes from the following observation, very startling: that any form of energy, light or any other energy, is made out of small lumps of energy that cannot be divided further -- so the word 'quantum,' quanta, lumps of energy that cannot be divided anymore.

It turns out that when you try to make measurements of very small particles like electrons, etc., to measure the position of the electron, you shine a light on it to see it.

When it hits, this light, the photon, must hit the electron and come back to your eye so you can see the electron. But because the electron is so small a lump of energy, it gives it such a big kick that it completely changes its state.

It means that every measurement in the quantum domain, of a microscopic particle, must introduce disturbance. It's called an uncertainty principle.

We can say, the more you try to find the position of a particle, the more you disturb its velocity. The more information you get, the more disturbance you do.

What I discovered was a new approach. Something very funny happens when you try to collect very, very little information. The disturbance becomes even more little if you are willing to do the experiment very gently, and repeat the experiment many, many times.

We find that with weak measurements, we can remove the disturbance, and see new things.

Q. What can you see that was not visible before?

A. It turns out that if you look at a particle, like an electron, a negatively charged particle, in a number of different locations, by doing pre- and post-selection measurements (before and after a single position has been selected by the experimenter), in the middle you find a particle that has very interesting properties. It can be accompanied by pairs of other particles -- you usually don't see them. Some of them behave the opposite way.

You see lots of new, rich phenomena once you learn to look at this with weak measurements. It's something we call the Cheshire cat effect. He got angry, and slowly disappeared; the only thing left behind was the smile of the cat.

The question is, how could there be the smile without the cat? We discovered the meaning of that by doing these weak measurements. We find the electron has a spin; the electron is in one location, but the spin sits in another place. The spin is like the smile of the cat.

We find lots of new, interesting phenomena looking in this new way with weak measurements. We get information about the present from the past and future.

Q. How do you explain to a lay audience the Aharonov-Bohm effect?

A. One of the basic features of physics is the issue of force. In classical physics, Newton's laws, we have a particle that doesn't experience any force and continues to move at the same velocity. The basic notion of these interactions was a complete absolute certainty in classical physics: in order for the particle to experience a force, the particle must be in the same location where the force is.

It turns out that in the factor we discovered, when the force is in one place, and the particle is moving far away from the force, the particle is affected. It's a new kind of non-locality that does not exist in classical physics.

You can have, for example, something called a magnetic field. You put the magnetic field in one region -- the magnet in one region of space -- and it is usual to think the particle must come to the place where the magnetic field is in order to experience the magnet.

We found that a quantum particle can move far away from the magnet, and even though it moves in a place where there is no magnetic field at all (it is still affected by the field).

This can happen only because of (quantum) uncertainty.

Q. What are you working on now?

A. Trying to understand further the consequences of this new approach to time -- all kinds of ideas on how to continue to change physics to accommodate this new approach. There are many possibilities. Just wish me luck.

Q. Were you born and raised in Israel?

A. Yes. Born in Israel, served in the army. Got my first degree at (Technion - Israel Institute of Technology in) Haifa, met David Bohm (co-discoverer of the Aharonov-Bohm effect), went with him to (Bristol University in) England, where I did my PhD.

Q. What pointed you in the direction of physics?

A. I was interested in deep questions. I found that physics can give me answers better than philosophy or religion. That's why I went into physics. All young children, when they are 10 or 12, are interested in deep questions.

What is the meaning of why we are here? What is the meaning of life? Do we have free will, etc.?

At 16 or 17 years old, at that time I was trying to find the answers by reading philosophy books -- eastern philosophy, mystery. But I found none of those get many answers.

But then I found two books on physics, translated into Hebrew. One was by Einstein, called Modern Physics. The other book was by (Arthur) Eddington, The Nature of the Physical World. There I discovered some deep questions, but they also have some clues to answer them. That convinced me to study physics, in order to answer those questions.

Q. What brought you to Chapman?

A. I was looking for a place where I can interact with people interested in deep questions. Menas (Kafatos, founding dean of the Schmid College of Science) was a person also interested in the same questions I'm interested in: how to explain our mind, our thinking, our consciousness. I was impressed with that. I liked very much (Chapman chancellor) Daniele Struppa. I was looking for a place where the higher-up people, the administrators, would be sympathetic to my work -- to do my own research without unnecessary interruptions from administrators.

Q. What is the importance of receiving the National Medal of Science?

A. People now think it will be much easier to get young people to work in this field if they see the field is recognized, that it is now a fruitful field. The medal is the beginning of recognition in this field, more than the recognition in the past -- the foundation of physics.

The most mysterious theory is quantum mechanics, therefore most of the work is in the foundation of quantum mechanics. It means trying to understand the most important features of physical theory, and not the details. The deeper questions. What does time mean? What does space mean? What do interactions mean? How do we go from the microscopic world to the macroscopic world? Can we explain ourselves (as) due to just interacting particles? Questions of this type interest me. The big question is whether physics is rich enough to explain us as physical systems.

Q. What were your impressions of President Obama?

A. We only exchanged a few words. My impression was a very warm person. He said some complimentary things to me. We did not really have a chance to talk more than that. But I got a very warm feeling from him. It was a very rewarding experience.

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